Why frankfort horizontal plane is used in facebow transfer?

Answer 1

The plane defined by the upper border of the bony auditory meatus (porion) bilaterally and the lowest point of the left orbit rim (orbitale) was accepted by the World Congress on Anthropology (Frankfurt) in 1884 as the horizontal reference for human craniometrics. As the science of Gnathology was developed in the 1920s (Charles Stuart, B. B. McCullum, and others) and sophisticated articulator technology to support it, the Frankfort was accepted (by convention) as the reference plane for orientation of the maxillary cast to the upper member of the articulator. All fully- or semi-adjustable articulator systems incorporate a device (usually, facebow or earbow) to record the relationship of the maxillary dental arch to these three points to transfer that relationship to the maxillary cast and articulator.